﻿using System;
using System.Collections;
using System.Collections.Generic;

namespace Microsoft.Practices.CompositeUI.Collections
{
    /// <summary>
    /// 	Represents a set of items. Adding an item to a set twice will only yield one instance
    /// 	in the collection.
    /// </summary>
    /// <typeparam name = "TItem">The type of items to be stored in the <see cref = "Set{TItem}" />.</typeparam>
    public class Set<TItem> : ICollection<TItem>
    {
        #region Fields & Properties

        private readonly Dictionary<TItem, object> _innerDictionary;
        private readonly bool _isReadOnly;

        #endregion

        #region Constructors

        public Set()
        {
            _innerDictionary = new Dictionary<TItem, object>();
            _isReadOnly = false;
        }

        private Set(Set<TItem> innerSet)
        {
            _innerDictionary = innerSet._innerDictionary;
            _isReadOnly = true;
        }

        #endregion

        #region Implementation of IEnumerable

        /// <summary>
        /// 	Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns>
        /// 	A <see cref = "T:System.Collections.Generic.IEnumerator`1" /> that can be used to iterate through the collection.
        /// </returns>
        /// <filterpriority>1</filterpriority>
        public IEnumerator<TItem> GetEnumerator()
        {
            return _innerDictionary.Keys.GetEnumerator();
        }

        /// <summary>
        /// 	Returns an enumerator that iterates through a collection.
        /// </summary>
        /// <returns>
        /// 	An <see cref = "T:System.Collections.IEnumerator" /> object that can be used to iterate through the collection.
        /// </returns>
        /// <filterpriority>2</filterpriority>
        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        #endregion

        #region Implementation of ICollection<TItem>

        /// <summary>
        /// 	Adds an item to the <see cref = "T:System.Collections.Generic.ICollection`1" />.
        /// </summary>
        /// <param name = "item">The object to add to the <see cref = "T:System.Collections.Generic.ICollection`1" />.</param>
        /// <exception cref = "T:System.NotSupportedException">The <see cref = "T:System.Collections.Generic.ICollection`1" /> is read-only.</exception>
        public void Add(TItem item)
        {
            if (IsReadOnly)
            {
                throw new NotSupportedException();
            }
            _innerDictionary[item] = String.Empty;
        }

        /// <summary>
        /// 	Removes all items from the <see cref = "T:System.Collections.Generic.ICollection`1" />.
        /// </summary>
        /// <exception cref = "T:System.NotSupportedException">The <see cref = "T:System.Collections.Generic.ICollection`1" /> is read-only. </exception>
        public void Clear()
        {
            if (IsReadOnly)
            {
                throw new NotSupportedException();
            }
            _innerDictionary.Clear();
        }

        /// <summary>
        /// 	Determines whether the <see cref = "T:System.Collections.Generic.ICollection`1" /> contains a specific value.
        /// </summary>
        /// <returns>
        /// 	true if <paramref name = "item" /> is found in the <see cref = "T:System.Collections.Generic.ICollection`1" />; otherwise, false.
        /// </returns>
        /// <param name = "item">The object to locate in the <see cref = "T:System.Collections.Generic.ICollection`1" />.</param>
        public bool Contains(TItem item)
        {
            return _innerDictionary.ContainsKey(item);
        }

        /// <summary>
        /// 	Copies the elements of the <see cref = "T:System.Collections.Generic.ICollection`1" /> to an <see
        ///  	cref = "T:System.Array" />, starting at a particular <see cref = "T:System.Array" /> index.
        /// </summary>
        /// <param name = "array">The one-dimensional <see cref = "T:System.Array" /> that is the destination of the elements copied from <see
        ///  	cref = "T:System.Collections.Generic.ICollection`1" />. The <see cref = "T:System.Array" /> must have zero-based indexing.</param>
        /// <param name = "arrayIndex">The zero-based index in <paramref name = "array" /> at which copying begins.</param>
        /// <exception cref = "T:System.ArgumentNullException"><paramref name = "array" /> is null.</exception>
        /// <exception cref = "T:System.ArgumentOutOfRangeException"><paramref name = "arrayIndex" /> is less than 0.</exception>
        /// <exception cref = "T:System.ArgumentException"><paramref name = "array" /> is multidimensional.-or-The number of elements in the source <see
        ///  	cref = "T:System.Collections.Generic.ICollection`1" /> is greater than the available space from <paramref
        ///  	name = "arrayIndex" /> to the end of the destination <paramref name = "array" />.-or-Type cannot be cast automatically to the type of the destination <paramref
        ///  	name = "array" />.</exception>
        public void CopyTo(TItem[] array, int arrayIndex)
        {
            _innerDictionary.Keys.CopyTo(array, arrayIndex);
        }

        /// <summary>
        /// 	Removes the first occurrence of a specific object from the <see cref = "T:System.Collections.Generic.ICollection`1" />.
        /// </summary>
        /// <returns>
        /// 	true if <paramref name = "item" /> was successfully removed from the <see
        ///  	cref = "T:System.Collections.Generic.ICollection`1" />; otherwise, false. This method also returns false if <paramref
        ///  	name = "item" /> is not found in the original <see cref = "T:System.Collections.Generic.ICollection`1" />.
        /// </returns>
        /// <param name = "item">The object to remove from the <see cref = "T:System.Collections.Generic.ICollection`1" />.</param>
        /// <exception cref = "T:System.NotSupportedException">The <see cref = "T:System.Collections.Generic.ICollection`1" /> is read-only.</exception>
        public bool Remove(TItem item)
        {
            if (IsReadOnly)
            {
                throw new NotSupportedException();
            }
            return _innerDictionary.Remove(item);
        }

        /// <summary>
        /// 	Gets the number of elements contained in the <see cref = "T:System.Collections.Generic.ICollection`1" />.
        /// </summary>
        /// <returns>
        /// 	The number of elements contained in the <see cref = "T:System.Collections.Generic.ICollection`1" />.
        /// </returns>
        public int Count
        {
            get
            {
                return _innerDictionary.Count;
            }
        }

        /// <summary>
        /// 	Gets a value indicating whether the <see cref = "T:System.Collections.Generic.ICollection`1" /> is read-only.
        /// </summary>
        /// <returns>
        /// 	true if the <see cref = "T:System.Collections.Generic.ICollection`1" /> is read-only; otherwise, false.
        /// </returns>
        public bool IsReadOnly
        {
            get
            {
                return _isReadOnly;
            }
        }

        #endregion

        #region As ReadOnly

        /// <summary>
        /// 	Returns a read-only wrapper around the <see cref = "Set{TItem}" />.
        /// </summary>
        public Set<TItem> AsReadOnly()
        {
            return new Set<TItem>(this);
        }

        #endregion
    }
}